PY2M20PY2M20Material Properties and Phase DiagramsL t 6Lecture 6
P. Stamenov, PhDS h l f Ph i TCDSchool of Physics, TCD
PY2M20-6
Microstructures i E t ti S t Iin Eutectic Systems: I
• Co < 2 wt% Sn• Result:
T(°C)400
L: Co wt% Sn
• Result:- at extreme ends
polycrystal of grains300 L
L
- polycrystal of grainsi.e., only one solid phase. L+
200 (Pb-Sn
100
TE(Pb SnSystem)
: Co wt% Sn
100 +
0Co, wt% Sn
10
2
20Co
30
(room T solubility limit)(room T solubility limit)
Microstructures i E t ti S t IIin Eutectic Systems: II
• 2 wt% Sn < Co < 18.3 wt% Sn• Result:
T(°C)400
L: Co wt% Sn
• Result: Initially liquid + then alone 300
LL then alone
finally two phases polycrystal
L +
200
: Co wt% Sn
polycrystal fine -phase inclusions
200TE
Pb-Snsystem
100+
y
Co , wt% Sn10
18 3
200Co
302
(sol limit at T ) 18.3(sol. limit at TE)
(sol. limit at Troom)
Microstructures i E t ti S t III• Co = CE
in Eutectic Systems: III Co CE
• Result: Eutectic microstructure (lamellar structure)- alternating layers (lamellae) of and crystals.g y ( ) y
Micrograph of Pb-Sn eutectic
i t t
T(°C)L: C wt% Sn microstructure
Pb-Snt
300 LL+
L: Co wt% Sn
systemL200
L 183°C
TE
Adapted from Fig 9 14 Callister 7e160m
100: 97.8 wt% Sn
Adapted from Fig. 9.14, Callister 7e.
20 60 80 1000 40
: 18.3 wt%Sn
C, wt% Sn0 60 80 000 0
18.3 97.8CE61.9
Lamellar Eutectic Structure
← Other possible eutectic structures are: rod-like, globular
and acicular.
Microstructures i E t ti S t IV
% S C % S
in Eutectic Systems: IV• 18.3 wt% Sn < Co < 61.9 wt% Sn• Result: crystals and an eutectic microstructure
C = 18.3 wt% Sn• Just above TE :T(°C) L: Co wt% Sn L
LCL = 61.9 wt% Sn
SR + S
W= = 50 wt%Pb-Snsystem
300 LL+
SR
SR
WL = (1- W) = 50 wt%R + S
• Just below TE :
systemL+200
TE
primary
Just below TE :C = 18.3 wt% SnC = 97.8 wt% Sn
100 +
18 3 61 9 97 8
eutectic eutectic
C 97.8 wt% SnS
R + SW= = 73 wt%
W 27 t%20 60 80 1000 40
18.3 61.9 97.8 W = 27 wt%Co, wt% Sn
Hypoeutectic & Hypereutectic
300 LL+
L+200
L
TE
(Pb-Sn S t )
T(°C)
+ 100
System)
Co, wt% Sn20 60 80 1000 40
hypereutectic: (illustration only)hypoeutectic: C = 50 wt% Sn 61 9eutectic
hypereutectic: (illustration only)
hypoeutectic: Co 50 wt% Sn 61.9
eutectic: Co =61.9wt% Sn
160 meutectic micro constituent
175 m
eutectic micro-constituent
Intermetallic Compounds
Mg PbMg2Pb
Note: intermetallic compound forms a line - not an area -Note: intermetallic compound forms a line not an area because the stoichiometry (i.e. composition) is exact.
Example: Eutectoid & Peritectic
Cu-Zn Phase diagramPeritectic transition + L
Cu-Zn Phase diagram
Eutectoid transition + Peritectoid – solid state PeritecticEutectoid transition + Peritectoid – solid state Peritectic
Eutectoid & Peritectic
E t t id lid h i ilib i Eutectoid - solid phase in equilibrium with two solid phaseswith two solid phasesS2 S1+S3 intermetallic compound
+ Fe3C (727ºC)
intermetallic compound - cementite
cool 3 ( )heat
Peritectic - liquid + solid 1 solid 2S + L SS1 + L S2
+ L (1493ºC)coolheat
περιτεκτικός → περι - included
Iron-Carbon Phase Diagram Extract
• 2 important 1600
T(°C)points
-Eutectic (A):
1600
1400 L
-Eutectoid (B):L +Fe3C
e)
1200 (austenite)
+LL+Fe3C1148°C
ASR
+Fe3C
emen
tit1000
800
+Fe3C
SR
e 3C
(ce800
600 +Fe C
727°C = Teutectoid
R SB
Fe
4000 1 2 3 4 5 6 6.7
+Fe3C
(Fe) C wt% C4.300 76α – bcc (FM)β bcc (NM) obs (Fe) Co, wt% C4.300.76
tect
oid Fe3C (cementite-hard)
(ferrite-soft)
β – bcc (NM) obs.γ – fcc (NM)δ bcc (NM)
Ceu
t ( )δ – bcc (NM)ε – hcp (p >13 GPa)
Pearlite
Fe3C (cementite-hard)
(ferrite-soft)
Result: Pearlite = 120 m
alternating layers of and Fe3C phases3 p
Hypoeutectoid Steel
1600
T(°C)
1400 L
+L
(Fe-C System)
entit
e)
1200
1000
(austenite)
+ Fe C
L+Fe3C1148°C
C (c
eme
800
+ Fe3C
727°Cr s
Fe3C600
400
+ Fe3C
w =s/(r+s)w =(1- w)
4000 1 2 3 4 5 6 6.7(Fe) Co, wt% CC0
0.76
pearlite
w =S/(R+S)wF C =(1-w)
wpearlite = wpearlite
wFe3C (1 w)
Hypoeutectoid Steel
100
lit 100 mw =S/(R+S)w C = (1 w)
wpearlite = wpearlite
wFe3C = (1-w)
Proeutectoidferrite
pearlite
proeutectoid phase – the first phase that forms upon cooling the solid
Hypereutectoid Steel
T(°C)1600
1400 L
T( C)(Fe-C System)
te)
1400
1200 (austenite)
+LL+Fe3C1148°C
emen
tit
1000
( )
+Fe3CFe3C
Fe3C
(ce800
600 +Fe C R S
sr
wF C =r/(r+s)
Fe3C
F
4000 1 2 3 4 5 6 6.7
+Fe3C
(Fe) C wt%C.76
Co
pearlite
wFe3C =r/(r+s)w =(1-w Fe3C)
(Fe) Co, wt%C0.
w =S/(R+S)w =(1 w )
wpearlite = wpearlite
wFe3C =(1-w)
Hypereutectoid Steel
pearlite
w =S/(R+S)wFe C =(1-w)
wpearlite = wp
Fe3C ( )
60 m60 m
proeutectoid Fe3Cpearlite
Example
For a 99 6 wt% Fe-0 40 wt% C at aFor a 99.6 wt% Fe-0.40 wt% C at a temperature just below the eutectoid, determine the following
a) the amount of pearlite anda) the amount of pearlite and proeutectoid ferrite () per 100 g of steel
b) composition of Fe C and ferrite ()b) composition of Fe3C and ferrite ()c) the amount of carbide (cementite) in ) ( )
grams that forms per 100 g of steel
Solutiona. the amount of pearlite and proeutectoid ferrite ()
t t f lit t f j t b Tnote: amount of pearlite = amount of just above TE
Co = 0.40 wt% CCo 0.40 wt% CC = 0.022 wt% CCpearlite = C = 0.76 wt% C 1600
Co C x 100 51.2 g e)
1400
1200
L
+LL+Fe3C1148°C
T(°C)
C Cx 100 51.2 g
emen
tit
1200
1000
(austenite)
+ Fe3C
L+Fe3C1148 C
pearlite = 51 2 g e 3C
(ce
800
600 + Fe C
727°CR S
pearlite 51.2 gproeutectoid = 48.8 g
F600
4000 1 2 3 4 5 6 6.7
+ Fe3C
C wt% CCOCC Co, wt% CCO
Solution - continuedb) composition of Fe3C and ferrite ()c) the amount of carbide
(cementite) in grams that CO = 0.40 wt% CC = 0.022 wt% CC 6 70 t% Cforms per 100 g of steel CFe C = 6.70 wt% C
31600
100xCFe
CFe
CFe3
3
3
CC
CCo
e)
1400
1200
L
+LL+Fe3C1148°C
T(°C)
g7.5100 022.07.6022.04.0
3
x
emen
tit
1200
1000
(austenite)
+ Fe3C
L+Fe3C1148 C
g 5.7 CFe3 e 3C
(ce
800
600 + Fe C
727°CR S
g 3.943
F600
4000 1 2 3 4 5 6 6.7
+ Fe3C
C wt% CCO CFe CC Co, wt% CCO CFe C3C
Alloying Steel with More Elements
• Teutectoid changes: • Ceutectoid changes:
) TiMo
Si
C)
d(°
C Mo W
(wt%
C NiCr
utec
toid Cr
M toid Si
MnW
TE
u
NiMn
Ceu
tect
TiW
Mo
wt. % of alloying elements wt. % of alloying elements
C
Taxonomy of MetalsMetal Alloys
Ferrous Nonferrous
Cu Al Mg TiSteels<1.4wt%C
Cast Irons3-4.5wt%C
1600
T(°C) microstructure:ferrite, graphite cementite
1400
1200
L
+L
L+Fe3C
1148°C
cementite
Fe3C
1000
800
austenite
+Fe3C
Eutectic:4.30
727°C Fe3C cementite
800
600
ferrite
+Fe3CEutectoid:
0.76
727°C
4000 1 2 3 4 5 6 6.7
(Fe) Co , wt% C
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